Concrete Material Estimate

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Using the Post Hole Calculator

The post hole calculator will determine the cubic yardage and bags of concrete needed for a concrete project involving a set of post holes. In addition, the calculator will estimate the number of pre-mixed bags of concrete needed for set of post holes.

Calculate the yards and bags of concrete needed by measuring the post holes using imperial or metric measurements, including inches, feet, yards, centimeters, or meters. Find out the number of 40 pound, 60 pound, or 80 pound bags of concrete are needed for the same set of post holes. Note that the post hole calculator is only an estimate, and while it can help find the amount of concrete needed, it is recommended to order additional material to account for settling and spillage. Concrete contractors can give estimates for delivering and installing cement for your post project.

Find the Amount of Concrete Needed

Concrete is sold by the cubic yard, or in pre-mixed bags. A cubic yard is just a standard volume, measured in yards. Find cubic yardage by multiplying width, length, and height of the project area. If you aren’t measuring in yards, convert all measurements to yards first, then multiply.

Identify the diameter and height of the post holes. If there are multiple different size post holes that need to be filled, calculate each set with matching dimensions separately and add the totals all together.

Find the cubic footage of each post hole. Find the radius by multiplying the diameter by 2. Get the radius to the second power by multiplying the radius times the radius. Then multiply by pi. Multiply the answer by the height.

pi x (diameter / 2)2 ) x height

If your posts will be going in the post holes, account for that volume and subtract from the cubic footage of each post. For instance, a 4×4 fence post is 3.5″ x 3.5″ at the full depth of the post hole, find that volume and subtract from the total size of the post hole to avoid having too much wasted concrete for the project.

It is necessary to convert the cubic footage to cubic yardage. To do so, divide the cubic footage by 27 to get the cubic yardage.

Multiply the cubic yardage by the quantity of post holes needed to find the total cubic yardage needed.

Suppliers will likely not sell fractions of a yard of concrete so you may need to round up to the nearest yard and order that amount. It is worthwhile to ask your supplier if they will sell a partial yard of material, but the most do not.

You can use bags of concrete for small projects when ordering a truck-load of concrete is not practical. A 60 pound bag of concrete will cover about .45 cubic feet and it would take about 60 bags to fill a cubic yard.

Circle/Cylinder

cubic yardage (yds3) = ( pi x (diameter / 2)2 ) x height

pi = 3.14159265359

Tips For Ordering Concrete

Call your concrete supplier and tell them about your project and what the concrete is for, ie. footings, fence posts, etc. Ask them to advise you on the proper mix given your application and region. They can tell you what will work best to support the strength requirements and freeze/thaw cycles in your region.

Consider additional costs for ready-mix concrete delivery. Typically, there are fees for delivery, weekend service, small loads, and overtime for long unloading times. Call your concrete supplier and understand these costs ahead of time and plan accordingly.

Order additional concrete for your project. The amount of overage you plan for will vary based on your quantity, but plan for at least 10% overage to accommodate spillage, settling, and grading inconsistencies. This will save you from a bad pour in the event that your estimates are even slightly off.

Remember to allocate enough time to dig all of the post holes for the project. Having concrete arrive before the holes are dug will result in significant waste or pouring concrete that has partially cured while digging the holes.

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